Unlike the terrestrial planets, Jupiter and Saturn exhibit differential rotation, See Why...

Observations of features like the Great Red Spot and smaller

storms allow astronomers to determine how rapidly Jupiter and

Saturn rotate. At its equator, Jupiter completes a full rotation in

only 9 hours, 50 minutes, and 28 seconds, making it not only the

largest and most massive planet in the solar system but also the

one with the fastest rotation. However, Jupiter rotates in a strikingly

different way from the Earth, the Moon, Mercury, Venus,

or Mars.

Differential Rotation:

If Jupiter were a solid body like a terrestrial planet (or, for that

matter, a billiard ball), all parts of Jupiter’s surface would rotate

through one complete circle in this same amount of time (Figure

12-3a). But by watching features in Jupiter’s cloud cover, Gian

Domenico Cassini discovered in 1690 that the polar regions of

the planet rotate a little more slowly than do the equatorial regions.

(You may recall this Italian astronomer from Section 11-2

as the gifted observer who first determined Mars’s rate of rotation.)

Near the poles, the rotation period of Jupiter’s atmosphere

is about 9 hours, 55 minutes, and 41 seconds. Saturn, too, has alonger rotation period near its poles (10 hours, 39 minutes, and

24 seconds) than at its equator (10 hours, 13 minutes, and

59 seconds).

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